The present invention relates generally to the non-mechanical contact probing of electronic devices and in particular, to the non-mechanical contact measurement of electronic signals during electrical inspection of electronic devices.
The ability to measure and apply voltages and currents on patterned structures without having to establish mechanical contact is of importance to the functional (electrical) testing of semiconductor devices and flat panel displays, e.g., liquid crystal and organic light emitting diode displays, backplanes, and printed circuit boards, since non-mechanical contact probing minimizes the likelihood of damage to the device/panel under test and is also conducive to improved testing throughput.
Photon Dynamics, Inc. (PDI)/Orbotech's Voltage Imaging® optical system (VIOS), employ electro-optical transducers to translate the electrical fields on the devices under test into optical information recorded by an optical sensor. Other techniques provide an indirect measurement of the voltage on the devices under test by means of secondary electrons and require the devices to be placed in vacuum. These approaches are mostly geared towards voltage measurements and still require mechanical contacts to pads on the periphery of the devices in order to drive the signals used for inspection.
A separate class of inspection methods based on conductive plasmas has recently emerged. The main concept behind these methods is that a directional plasma, which contains mobile secondary electrons besides ions, may act as a non-mechanical contact probe. Several such “plasma probing” approaches have been proposed in the past. They may roughly be divided into two categories, one category being based on high intensity laser-induced ionization, which presents possible risks of laser-induced damage to the device under tests given the high ionization thresholds, and another category being based on high voltage corona discharges, in which ionized species have a wide range of scattering angles and also presents damage risks, especially related to arcing.
Electron beam imaging systems using membranes and differentially pumped apertures have been used to propagate e-beams into a gas ambient for electron beam characterization of live/wet specimens in scanning electron microscopes (SEM) or X-ray diffraction on live samples.